Ramp-Shaped RF Pulse for bSSFP MR Angiography Signal Decay
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Solution Overview
Problem
Current bSSFP imaging techniques face challenges in visualizing the full extent of blood vessels due to signal decay and unequal contrast caused by varying equilibrium states and excessive flip angle reductions, particularly when imaging moving blood, which limits the visualization of expanding vascular trees and results in reduced signal-to-noise ratio and inefficient background contrast stabilization.
Innovation Solution
The implementation of a temporally symmetrical ramp pulse with a lower flip angle on the inflow side and a monotonically increasing flip angle profile within the imaging volume, optimized for the bSSFP sequence, minimizes signal decay and maintains signal strength across the imaging volume by leveraging the T1 relaxation time being greater than T2, allowing for longer preservation of amplified MR signals and improved homogeneity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If a high flip angle is used to maximize signal strength, then the signal-to-noise ratio is improved, but the signal decay increases and the visualization distance of blood vessels is limited
Solution Approach 1:
The patent applies local quality by using a spatially varying flip angle profile where the flip angle changes monotonically from the inflow side to the outflow side of the imaging volume. This allows different regions to have optimized flip angles: lower angles at the inflow side to minimize decay and extend visualization distance, and higher angles at the outflow side to maintain signal strength, thereby resolving the contradiction between signal strength and visualization distance.
2Length of moving object
If the imaging volume is subdivided into multiple sub-volumes to minimize decay, then the signal decay is reduced, but the signal-to-noise ratio is reduced and background contrast stabilization becomes inefficient
Solution Approach 1:
The patent applies parameter changes by continuously varying the flip angle parameter across the imaging volume rather than using discrete subdivisions. This continuous parameter change allows for optimized signal decay compensation throughout the entire imaging volume while maintaining adequate signal-to-noise ratio and avoiding the inefficiencies of multiple sub-volumes and prescans.
3Length of moving object
If a monotonically increasing flip angle profile is used to extend visualization distance, then the signal decay is minimized, but excessive flip angle reduction causes signal losses
Solution Approach 1:
The patent resolves this contradiction by applying local quality through a spatially optimized flip angle profile that monotonically increases from inflow to outflow side. The profile is specifically designed to balance decay minimization with signal preservation, ensuring that flip angles are sufficiently low at the inflow side to extend visualization distance while being high enough at the outflow side to maintain adequate signal strength and avoid excessive signal losses.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach enhances the signal-to-noise ratio and enables longer acquisition times, allowing for clearer visualization of blood vessels and improved image quality, particularly in low-field magnetic resonance devices, by reducing phase drift and maintaining signal strength throughout the imaging volume.
Implementation Method 1
a magnetic resonance data recording method for recording magnetic resonance data from an imaging volume to be recorded
Implementation Method 2
the inverse of the decay rate to the equilibrium state is greater than the T1 relaxation time of the tissue/fluid
Implementation Method 3
the decay rate is a Flip angle-dependent mixture of T1 and T2
Implementation Method 4
radio frequency pulses that generate a changing flip angle across the imaging volume, which are referred to as ramp pulses or TONE pulses
Implementation Method 5
bSSFP (Balanced Steady-State Free Precession) imaging technique
Data Source
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AI summary
Method for recording magnetic resonance data from an imaging volume (1) of a patient in which fluid, in particular blood, is moving, using a bSSFP magnetic resonance sequence in which spins located within the imaging volume (1) are cyclically excited by means of a radio frequency pulse, with a magnetic resonance device (17), wherein the radio frequency pulse is a ramp pulse which sets a spatially variable flip angle of the spins within the imaging volume (1), wherein the flip angle on a side (4) from which the fluid flows into the imaging volume (1) is chosen to be lower than on the side (5) from which the fluid flows out, and increases monotonically.